diff --git a/config/arch/sh.in b/config/arch/sh.in
index 68d31200..60de3133 100644
--- a/config/arch/sh.in
+++ b/config/arch/sh.in
@@ -5,6 +5,7 @@
 ## select ARCH_USE_MMU
 ## select ARCH_SUPPORTS_BOTH_ENDIAN
 ## select ARCH_DEFAULT_LE
+## select ARCH_REQUIRES_MULTILIB
 ##
 ## help The Super-H architecture, as defined by:
 ## help     http://www.renesas.com/fmwk.jsp?cnt=superh_family_landing.jsp&fp=/products/mpumcu/superh_family/
diff --git a/config/cc/gcc.in.2 b/config/cc/gcc.in.2
index 17b41ccf..c200d22c 100644
--- a/config/cc/gcc.in.2
+++ b/config/cc/gcc.in.2
@@ -37,6 +37,16 @@ config CC_GCC_EXTRA_CONFIG_ARRAY
       if they are properly quoted (or escaped, but prefer quotes). Eg.:
           --with-foo="1st arg with 4 spaces" --with-bar=2nd-arg-without-space
 
+config CC_GCC_MULTILIB_LIST
+    string
+    prompt "List of multilib variants"
+    depends on MULTILIB
+    help
+      Architecture-specific option of expanding or restricting the list of
+      the multilib variants to be built. Refer to GCC installation manual
+      for the format of this option for a particular architecture.
+      Leave empty to use the default list for this architecture.
+
 config CC_GCC_TARGET_FINAL
     bool
     prompt "Use the default targets all and install for the final compiler"
diff --git a/config/libc/musl.in b/config/libc/musl.in
index 00d98eae..ff84448b 100644
--- a/config/libc/musl.in
+++ b/config/libc/musl.in
@@ -1,6 +1,7 @@
 # musl options
 
 ## depends on ! WINDOWS && ! BARE_METAL
+## depends on EXPERIMENTAL
 ##
 ## select LIBC_SUPPORT_THREADS_NATIVE
 ## select CC_CORE_PASSES_NEEDED
diff --git a/scripts/build/arch/alpha.sh b/scripts/build/arch/alpha.sh
index cf6d40d9..ffceae3d 100644
--- a/scripts/build/arch/alpha.sh
+++ b/scripts/build/arch/alpha.sh
@@ -4,3 +4,14 @@ CT_DoArchTupleValues () {
     # The architecture part of the tuple:
     CT_TARGET_ARCH="${CT_ARCH}${CT_ARCH_SUFFIX:-${CT_ARCH_ALPHA_VARIANT}}"
 }
+
+#------------------------------------------------------------------------------
+# Get multilib architecture-specific target
+# Usage: CT_DoArchMultilibTarget "multilib flags" "target tuple"
+CT_DoArchMultilibTarget ()
+{
+    local target="${1}"; shift
+    local -a multi_flags=( "$@" )
+
+    echo "${target}"
+}
diff --git a/scripts/build/arch/arm.sh b/scripts/build/arch/arm.sh
index 5f6ce2fc..338392c3 100644
--- a/scripts/build/arch/arm.sh
+++ b/scripts/build/arch/arm.sh
@@ -39,3 +39,14 @@ CT_DoArchTupleValues() {
         CT_TARGET_SYS="${CT_TARGET_SYS}hf"
     fi
 }
+
+#------------------------------------------------------------------------------
+# Get multilib architecture-specific target
+# Usage: CT_DoArchMultilibTarget "multilib flags" "target tuple"
+CT_DoArchMultilibTarget ()
+{
+    local target="${1}"; shift
+    local -a multi_flags=( "$@" )
+
+    echo "${target}"
+}
diff --git a/scripts/build/arch/m68k.sh b/scripts/build/arch/m68k.sh
index bf26d1b2..a6eb010e 100644
--- a/scripts/build/arch/m68k.sh
+++ b/scripts/build/arch/m68k.sh
@@ -3,3 +3,14 @@
 CT_DoArchTupleValues() {
     :
 }
+
+#------------------------------------------------------------------------------
+# Get multilib architecture-specific target
+# Usage: CT_DoArchMultilibTarget "multilib flags" "target tuple"
+CT_DoArchMultilibTarget ()
+{
+    local target="${1}"; shift
+    local -a multi_flags=( "$@" )
+
+    echo "${target}"
+}
diff --git a/scripts/build/arch/microblaze.sh b/scripts/build/arch/microblaze.sh
index 456a6e3a..93ecc9a2 100644
--- a/scripts/build/arch/microblaze.sh
+++ b/scripts/build/arch/microblaze.sh
@@ -19,3 +19,14 @@ CT_DoArchTupleValues () {
     esac
 
 }
+
+#------------------------------------------------------------------------------
+# Get multilib architecture-specific target
+# Usage: CT_DoArchMultilibTarget "multilib flags" "target tuple"
+CT_DoArchMultilibTarget ()
+{
+    local target="${1}"; shift
+    local -a multi_flags=( "$@" )
+
+    echo "${target}"
+}
diff --git a/scripts/build/arch/mips.sh b/scripts/build/arch/mips.sh
index 4d732be9..68ad4faa 100644
--- a/scripts/build/arch/mips.sh
+++ b/scripts/build/arch/mips.sh
@@ -14,3 +14,14 @@ CT_DoArchTupleValues() {
     CT_ARCH_ABI_CFLAG="-mabi=${CT_ARCH_mips_ABI}"
     CT_ARCH_WITH_ABI="--with-abi=${CT_ARCH_mips_ABI}"
 }
+
+#------------------------------------------------------------------------------
+# Get multilib architecture-specific target
+# Usage: CT_DoArchMultilibTarget "multilib flags" "target tuple"
+CT_DoArchMultilibTarget ()
+{
+    local target="${1}"; shift
+    local -a multi_flags=( "$@" )
+
+    echo "${target}"
+}
diff --git a/scripts/build/arch/powerpc.sh b/scripts/build/arch/powerpc.sh
index fbc3120f..77bbc8a2 100644
--- a/scripts/build/arch/powerpc.sh
+++ b/scripts/build/arch/powerpc.sh
@@ -26,3 +26,44 @@ CT_DoArchTupleValues () {
         CT_ARCH_CC_EXTRA_CONFIG="--enable-e500_double"
     fi
 }
+#------------------------------------------------------------------------------
+# Get multilib architecture-specific target
+# Usage: CT_DoArchMultilibTarget "multilib flags" "target tuple"
+CT_DoArchMultilibTarget ()
+{
+    local target="${1}"; shift
+    local -a multi_flags=( "$@" )
+
+    local m32=false
+    local m64=false
+    local mlittle=false
+    local mbig=false
+
+    for m in "${multi_flags[@]}"; do
+        case "$m" in
+            -m32)     m32=true ;;
+            -m64)     m64=true ;;
+            -mbig)    mbig=true ;;
+            -mlittle) mlittle=true ;;
+        esac
+    done
+
+    # Fix up bitness
+    case "${target}" in
+        powerpc-*)      $m64 && target=${target/#powerpc-/powerpc64-} ;;
+        powerpcle-*)    $m64 && target=${target/#powerpcle-/powerpc64le-} ;;
+        powerpc64-*)    $m32 && target=${target/#powerpc64-/powerpc-} ;;
+        powerpc64le-*)  $m32 && target=${target/#powerpc64le-/powerpcle-} ;;
+    esac
+
+    # Fix up endianness
+    case "${target}" in
+        powerpc-*)      $mlittle && target=${target/#powerpc-/powerpcle-} ;;
+        powerpcle-*)    $mbig && target=${target/#powerpcle-/powerpc-} ;;
+        powerpc64-*)    $mlittle && target=${target/#powerpc64-/powerpc64le-} ;;
+        powerpc64le-*)  $mbig && target=${target/#powerpc64le-/powerpc64-} ;;
+    esac
+
+    # return the target
+    echo "${target}"
+}
diff --git a/scripts/build/arch/s390.sh b/scripts/build/arch/s390.sh
index b4b8078c..e303420a 100644
--- a/scripts/build/arch/s390.sh
+++ b/scripts/build/arch/s390.sh
@@ -6,3 +6,30 @@ CT_DoArchTupleValues() {
         CT_TARGET_ARCH="s390x${CT_ARCH_SUFFIX}"
     fi
 }
+
+#------------------------------------------------------------------------------
+# Get multilib architecture-specific target
+# Usage: CT_DoArchMultilibTarget "multilib flags" "target tuple"
+CT_DoArchMultilibTarget ()
+{
+    local target="${1}"; shift
+    local -a multi_flags=( "$@" )
+
+    local m31=false
+    local m64=false
+
+    for m in "${multi_flags[@]}"; do
+        case "${multi_flags}" in
+            -m64) m64=true ;;
+            -m31) m31=true ;;
+        esac
+    done
+
+    # Fix bitness
+    case "${target}" in
+        s390-*)   $m64 && target=${target/#s390-/s390x-} ;;
+        s390x-*)  $m31 && target=${target/#s390x-/s390-} ;;
+    esac
+
+    echo "${target}"
+}
diff --git a/scripts/build/arch/sh.sh b/scripts/build/arch/sh.sh
index 7780e40f..e7f4f1a4 100644
--- a/scripts/build/arch/sh.sh
+++ b/scripts/build/arch/sh.sh
@@ -35,3 +35,14 @@ CT_DoArchTupleValues () {
     esac
     CT_ARCH_FLOAT_CFLAG=
 }
+
+#------------------------------------------------------------------------------
+# Get multilib architecture-specific target
+# Usage: CT_DoArchMultilibTarget "multilib flags" "target tuple"
+CT_DoArchMultilibTarget ()
+{
+    local target="${1}"; shift
+    local -a multi_flags=( "$@" )
+
+    echo "${target}"
+}
diff --git a/scripts/build/arch/sparc.sh b/scripts/build/arch/sparc.sh
index e3e74913..2d3baa35 100644
--- a/scripts/build/arch/sparc.sh
+++ b/scripts/build/arch/sparc.sh
@@ -2,4 +2,28 @@
 CT_DoArchTupleValues() {
     # That's the only thing to override
     CT_TARGET_ARCH="sparc${target_bits_64}${CT_ARCH_SUFFIX}"
+
+    # By default, sparc64-*-linux is configured with -mcpu=v9. However,
+    # according to https://sourceware.org/ml/libc-alpha/2005-12/msg00027.html,
+    # "There is no Linux sparc64 port that runs on non-UltraSPARC-I+ ISA CPUs."
+    # There is a patch that would change the default to -mcpu=ultrasparc for
+    # sparc64-*-linux configuration: https://patchwork.ozlabs.org/patch/409424/
+    # but that patch has not been integrated (yet). One concern raised about
+    # this patch was that -mcpu=ultrasparc can suboptimally schedule instructions
+    # for newer SPARC CPUs. So, override to -mcpu=ultrasparc and warn the user.
+    if [ "${CT_KERNEL}" = "linux" -a "${CT_ARCH_64}" = "y" -a -z "${CT_ARCH_CPU}" ]; then
+        CT_DoLog WARN "Setting CPU to UltraSPARC-I for sparc64-linux. Set CT_ARCH_CPU if a different CPU is desired."
+        CT_ARCH_WITH_CPU="--with-cpu=ultrasparc"
+    fi
+}
+
+#------------------------------------------------------------------------------
+# Get multilib architecture-specific target
+# Usage: CT_DoArchMultilibTarget "multilib flags" "target tuple"
+CT_DoArchMultilibTarget ()
+{
+    local target="${1}"; shift
+    local -a multi_flags=( "$@" )
+
+    echo "${target}"
 }
diff --git a/scripts/build/arch/x86.sh b/scripts/build/arch/x86.sh
index 69407db9..ca0f08bf 100644
--- a/scripts/build/arch/x86.sh
+++ b/scripts/build/arch/x86.sh
@@ -20,4 +20,51 @@ CT_DoArchTupleValues() {
         esac
     fi
     CT_TARGET_ARCH="${CT_TARGET_ARCH}${CT_ARCH_SUFFIX}"
+
+    # Shouldn't be possible to specify this (CT_TARGET_SYS is not specified by the user,
+    # it is computed by scripts/functions from libc choices). But trap if such invalid
+    # values ever come from the caller:
+    case "${CT_TARGET_ARCH}-${CT_TARGET_SYS}" in
+        i[34567]86-gnux32)
+            CT_DoLog ERROR "Invalid CT_TARGET: i[34567]86-<vendor>-<os>-gnux32 is invalid."
+            CT_DoLog ERROR "CT_TARGET: ${CT_TARGET}"
+            CT_Abort "Go read: https://wiki.debian.org/Multiarch/Tuples"
+            ;;
+    esac
+}
+
+#------------------------------------------------------------------------------
+# Get multilib architecture-specific target
+# Usage: CT_DoArchMultilibTarget "multilib flags" "target tuple"
+CT_DoArchMultilibTarget ()
+{
+    local target="${1}"; shift
+    local -a multi_flags=( "$@" )
+
+    local bit32=false
+    local bit64=false
+    local abi_dflt=false
+    local abi_x32=false
+
+    for m in "${multi_flags[@]}"; do
+        case "$m" in
+            -m32)  bit32=true; abi_dflt=true;;
+            -m64)  bit64=true; abi_dflt=true;;
+            -mx32) bit64=true; abi_x32=true;;
+        esac
+    done
+
+    # Fix up architecture.
+    case "${target}" in
+        x86_64-*)      $bit32 && target=${target/#x86_64-/i386-} ;;
+        i[34567]86-*)  $bit64 && target=${target/#i[34567]86-/x86_64-} ;;
+    esac
+
+    # Fix up the ABI part.
+    case "${target}" in
+        *x32) $abi_dflt && target=${target/%x32} ;;
+        *)    $abi_x32  && target=${target}x32 ;;
+    esac
+
+    echo "${target}"
 }
diff --git a/scripts/build/cc/100-gcc.sh b/scripts/build/cc/100-gcc.sh
index 7085a904..7bb3610f 100644
--- a/scripts/build/cc/100-gcc.sh
+++ b/scripts/build/cc/100-gcc.sh
@@ -403,10 +403,20 @@ do_gcc_core_backend() {
         extra_config+=("--with-system-zlib")
     fi
 
-    # Some versions of gcc have a deffective --enable-multilib.
-    # Since that's the default, only pass --disable-multilib.
+    # Some versions of gcc have a defective --enable-multilib.
+    # Since that's the default, only pass --disable-multilib. For multilib,
+    # also enable multiarch. Without explicit --enable-multiarch, pass-1
+    # compiler is configured as multilib/no-multiarch and pass-2/final
+    # are multilib/multiarch (because gcc autodetects multiarch based on
+    # multiple instances of crt*.o in the install directory - which do
+    # not exist in pass-1).
     if [ "${CT_MULTILIB}" != "y" ]; then
         extra_config+=("--disable-multilib")
+    else
+        extra_config+=("--enable-multiarch")
+        if [ -n "${CT_CC_GCC_MULTILIB_LIST}" ]; then
+            extra_config+=("--with-multilib-list=${CT_CC_GCC_MULTILIB_LIST}")
+        fi
     fi
 
     CT_DoLog DEBUG "Extra config passed: '${extra_config[*]}'"
@@ -880,10 +890,15 @@ do_gcc_backend() {
         extra_config+=("--with-system-zlib")
     fi
 
-    # Some versions of gcc have a deffective --enable-multilib.
+    # Some versions of gcc have a defective --enable-multilib.
     # Since that's the default, only pass --disable-multilib.
     if [ "${CT_MULTILIB}" != "y" ]; then
         extra_config+=("--disable-multilib")
+    else
+        extra_config+=("--enable-multiarch")
+        if [ -n "${CT_CC_GCC_MULTILIB_LIST}" ]; then
+            extra_config+=("--with-multilib-list=${CT_CC_GCC_MULTILIB_LIST}")
+        fi
     fi
 
     CT_DoLog DEBUG "Extra config passed: '${extra_config[*]}'"
diff --git a/scripts/build/libc/glibc.sh b/scripts/build/libc/glibc.sh
index 013c6ebd..472acad4 100644
--- a/scripts/build/libc/glibc.sh
+++ b/scripts/build/libc/glibc.sh
@@ -137,7 +137,7 @@ do_libc_backend() {
 
         CT_mkdir_pushd "${CT_BUILD_DIR}/build-libc-${libc_mode}${extra_dir//\//_}"
 
-        target=${CT_TARGET}
+        target=$( CT_DoMultilibTarget "${CT_TARGET}" ${extra_flags} )
         case "${target}" in
             # SPARC quirk: glibc 2.23 and newer dropped support for SPARCv8 and
             # earlier (corresponding pthread barrier code is missing). Until this
@@ -147,6 +147,18 @@ do_libc_backend() {
                     target=${target/#sparc-/sparcv9-}
                 fi
                 ;;
+            # x86 quirk: architecture name is i386, but glibc expects i[4567]86 - to
+            # indicate the desired optimization. If it was a multilib variant of x86_64,
+            # then it targets at least NetBurst a.k.a. i786, but we'll follow arch/x86.sh
+            # and set the optimization to i686. Otherwise, replace with the most
+            # conservative choice, i486.
+            i386-*)
+                if [ "${CT_TARGET_ARCH}" = "x86_64" ]; then
+                    target=${target/#i386-/i686-}
+                else
+                    target=${target/#i386-/i486-}
+                fi
+                ;;
         esac
 
         do_libc_backend_once extra_dir="${extra_dir}"               \
@@ -193,6 +205,7 @@ do_libc_backend() {
 #   libc_full           : Build full libc                       : bool      : n
 #   extra_flags         : Extra CFLAGS to use (for multilib)    : string    : (empty)
 #   extra_dir           : Extra subdir for multilib             : string    : (empty)
+#   target              : Build libc using this target (for multilib) : string : ${CT_TARGET}
 do_libc_backend_once() {
     local libc_headers
     local libc_startfiles
@@ -213,6 +226,10 @@ do_libc_backend_once() {
         eval "${arg// /\\ }"
     done
 
+    if [ "${target}" = "" ]; then
+        target="${CT_TARGET}"
+    fi
+
     CT_DoLog EXTRA "Configuring C library"
 
     case "${CT_LIBC}" in
@@ -288,12 +305,12 @@ do_libc_backend_once() {
                      |${sed} -r -e '/^(.*[[:space:]])?-(E[BL]|m((big|little)(-endian)?|e?[bl]))([[:space:]].*)?$/!d;' \
                                 -e 's//\2/;'    \
                    )"
+    # If extra_flags contained an endianness option, no need to add it again. Otherwise,
+    # add the option from the configuration.
     case "${endian_extra}" in
         EB|mbig-endian|mbig|meb|mb)
-            extra_cc_args="${extra_cc_args} ${endian_extra}"
             ;;
         EL|mlittle-endian|mlittle|mel|ml)
-            extra_cc_args="${extra_cc_args} ${endian_extra}"
             ;;
         "") extra_cc_args="${extra_cc_args} ${CT_ARCH_ENDIAN_OPT}"
             ;;
@@ -458,7 +475,8 @@ do_libc_backend_once() {
             # However, since we will never actually execute its code,
             # it doesn't matter what it contains.  So, treating '/dev/null'
             # as a C source file, we produce a dummy 'libc.so' in one step
-            CT_DoExecLog ALL "${cross_cc}" -nostdlib        \
+            CT_DoExecLog ALL "${cross_cc}" ${extra_flags}   \
+                                           -nostdlib        \
                                            -nostartfiles    \
                                            -shared          \
                                            -x c /dev/null   \
diff --git a/scripts/functions b/scripts/functions
index 70c1ba61..62d264e3 100644
--- a/scripts/functions
+++ b/scripts/functions
@@ -1305,6 +1305,25 @@ CT_DoBuildTargetTuple() {
     CT_ARCH_TARGET_LDFLAGS="${CT_ARCH_TARGET_LDFLAGS} ${CT_ARCH_ENDIAN_LDFLAG}"
 }
 
+# This function determines the target tuple for a given set of compiler
+# flags, using either GCC's multiarch feature (if supported; if not,
+# GCC prints nothing and exits with status 0), falling back to calling
+# the architecture-specific functions.
+CT_DoMultilibTarget() {
+    local target="$1"; shift
+    local -a multi_flags=( "$@" )
+    local gcc_multiarch
+
+    gcc_multiarch=$( "${CT_TARGET}-gcc" -print-multiarch "${multi_flags[@]}" )
+    if [ -n "${gcc_multiarch}" ]; then
+        echo "${gcc_multiarch}"
+        return
+    fi
+
+    # Fall back to arch-specific guesswork
+    CT_DoArchMultilibTarget "${target}" "${multi_flags[@]}"
+}
+
 # This function does pause the build until the user strikes "Return"
 # Usage: CT_DoPause [optional_message]
 CT_DoPause() {